In an image pick-up apparatus that normally has a lens system and an image pick-up unit, there is the risk of defects such as shading appearing in the picked-up photographic image due to peripheral light fall-off caused by the lens system, for example. The generation of such defects is prevented by designing a lens system so as to include multiple lenses, for example, though such lens systems that are composed of multiple lenses are expensive, so that in many cases such lens systems cannot be implemented in consumer appliances.
On the other hand, when signals are outputted in accordance with an X-Y coordinate system, as in the case with appliances that use semiconductor image pick-up devices for example, the image can be corrected by performing a digital process on the outputted signals. In the field of scanners and the like, for example, a variety of techniques have already been proposed for digitally compensating for lens shading, such as warping, peripheral light fall-off, and color bleeding that occur when image pick-up is performed with a cheap lens system (see Japanese Laid-Open Patent Application Nos. 11-355511, 2000-41183, etc.)
However, these conventional techniques can only be applied to the field of scanners and similar devices, where it is permissible for the compensation processing to take a fair amount of time and there are no demands for compensation to be performed in real-time as with the case of digital cameras, for example. On the other hand, as one example, Japanese Laid-Open Patent Application No. 2000-41179 proposes a technique for digitally compensating lens shading and the like in a digital camera.
In more detail, in an apparatus that performs image pick-up using a lens system, lens shading, such as warping, peripheral light fall-off, and color bleeding, is believed to be related to the distance from the optical axis of the lens system. For this reason, if the signals for pixels produced by image pick-up are corrected in accordance with this distance, a reduction can be made in lens shading, or the lens shading can be compensated for. Accordingly, to perform such compensation, it is necessary to first calculate how far a pixel to be corrected is located from the optical axis of the lens system.
However, in a conventional method for calculating the distance d from the optical axis of the lenses, the distance between the origin O and the correction target pixel is set as at x on the X coordinate axis and is set at y on the Y coordinate axis, and the distance is found as d=√(x2+y2) using Pythagoras' Theorem. However, since the calculation of squares and the calculation of a square root are performed, an extremely large circuit construction is required to realize a calculation means in hardware.
It should be noted that while the above calculations can be performed using software, there is the problem that such software calculations take too much time for the processing to be performed in real-time in a digital camera. While a technique (see Japanese Laid-Open Patent Application No. 7-95856) for performing the calculations using simplified hardware has been proposed, such calculations are not very precise, so that in order to correct luminance such as peripheral light fall-off, it becomes necessary to calculate distances with higher precision.
Also, with the above hardware-based calculation of distances, there is the risk that it will not be possible to correctly find the distance from the optical axis when there are changes in the size of the image pick-up unit or changes in the reading out method, such as when pixels are skipped in the case where a charge transfer device is used as the image pick-up unit. This is to say, when pixels are skipped as shown in FIG. 18A, the correction that is originally performed as shown in FIG. 18B becomes as shown in FIG. 18C, so that it is no longer possible to perform the correction correctly using fixed hardware.
The present application was conceived in view of the above, and attempts to solve the problems with conventional methods and apparatuses in that an extremely large circuit construction is required to realize a distance calculation means in hardware, in that a simplified circuit construction is not able to calculate distances with high precision, and in that it is not possible to correctly find the distance from the optical axis when there are changes in the reading out method, such as when the size of the image pick-up unit changes or when pixels are skipped.